The star and planet under scrutiny are known as HD189733 and HD189733b, respectively. The exoplanet was discovered in 2005 by Doppler spectroscopy. Astronomers were to infer the duration of orbital cycles and the probable size of a planet via Doppler spectroscopy, but hard data like orbital orientation and physical composition are much more difficult. Previous findings likened the planet to a hot Jupiter, orbiting very close to its star.

The astronomers used the 60cm KVA telescope, which resides in La Palma, Spain, by remote control to make their observations. The telescope is operated by Tuorla observatory by agreement with the Royal Swedish Academy of Science to which it belongs, and was modernized by Finnish scientists.

Rather than directly observing the light reflected from the planet's atmosphere, the group used a method similar to polarized glasses. Extraneous light was filtered from other sources and the reflection of HD189733's light from the atmosphere of HD189733b became visible, similar to the way we observe the sun's light reflecting off the surface of the moon.

The light reflected from HD189733b indicates that the atmosphere surrounding the planet is considerably larger than the planet itself, in the area of 30% or more, probably due to the heat of orbiting so closely to its star. Other data gathered seems to allude to the atmosphere being made up of very small particles such as atoms, molecules, tiny grains of dust and possibly water vapor. An atmosphere of this composition would effectively scatter blue light in the same way as Earth's.

The group has published their observations in a paper titled First Detection of Polarized Scattered Light From an Exoplanetary Atmosphere (PDF).